Abstract:Background: Rapid-mix flow cytometry has emerged as a powerful tool for mechanistic analysis of ligand binding, cell response, and molecular assembly. Although progress has come from improving sample delivery capabilities, little attention has been paid to the volumetric requirements associated with precious biological reagents. Methods: By using programmable syringes, valves, and other fluidic components, we created a modular, precisely regulated rapid-mix device for the delivery of small-volume samples to the flow cytometer. The device was tested using a bead-based assay in which the binding kinetics between native biotin and fluorescein biotin-bearing beads were characterized. Results: Bead suspensions and reagents paired in 35- to 45-mu l aliquots were efficiently mixed by the device and delivered to the flow cytometer. Kinetic data associated with the fluorescein biotin beads were analyzed and used to calibrate the performance characteristics of the device in terms of sample delivery and mixing efficiency. Conclusion: The rapid-mix device is capable of detecting subsecond kinetics of biological reactions using microliter volume of samples. Dimensions of the device have been minimized, and the quantitative aspects of sample delivery and analysis have been optimized. Further, the modular design has been optimized for adaptation to a variety of experimental protocols. (c) 2005 Wiley-Liss, Inc.